Race condition in AuthenticationHelper with React Native

[maxdavidson]

In c359661350c98fd0d25ec8f3cd5fd494c5a167d7, some functions were made asynchronous with the introduction of native bindings in React Native. generateHashDevice in AuthenticationHelper.js was given a callback parameter because of its use of modPow, but the callback is not used in CognitoUser.js

https://github.com/aws/amazon-cognito-identity-js/blob/c359661350c98fd0d25ec8f3cd5fd494c5a167d7/src/AuthenticationHelper.js#L137-L156

https://github.com/aws/amazon-cognito-identity-js/blob/c359661350c98fd0d25ec8f3cd5fd494c5a167d7/src/AuthenticationHelper.js#L126-L128

https://github.com/aws/amazon-cognito-identity-js/blob/c359661350c98fd0d25ec8f3cd5fd494c5a167d7/src/CognitoUser.js#L363-L374

This happens to work in the browser, since the callback is called synchronously. However, this will create an error in RN, because authenticationHelper.verifierDevices is accessed before it's assigned, and util.Buffer will be instantiated with undefined.

[itrestian]

React Native support was just released so we would have to look into it. You mentioned this doesn't happen in the browser, correct? Also if you disable device tracking in the console will it work?

[maxdavidson]

Turns out it doesn't work in the browser, because of the missing third callback parameter to authenticationHelper.generateHashDevice. It's the same problem causing #586 and #588.

[itrestian]

K, so in the browser we can add a check for the existence of callback.

[maxdavidson]

Or just add the callback so it works in as intended in the both the browser and RN

[itrestian]

Pull request with fix has been merged.

[dahudson88]

Beautiful!